The present invention relates to a shaft prosthesis which has another surface provided with grooves which extend generally along the length of the prosthesis and which have side walls forming an essentially wedge-shaped cross section terminating at a tip oriented toward a central longitudinal axis of the prosthesis. Each groove defines a plane; these planes intersect in the central longitudinal axis. The number of grooves in an angular region having a vertex on the center axis increases with increasing distance of the outer surface from the center axis.
Shaft prosthesis are known which have grooves extending in the longitudinal direction of the shaft. Similarly to the shaft prosthesis disclosed in European Patent No. 0.145,939, the grooves extend at equal distances from one another on the surface. During the appropriate manufacturing process, the milling cutter or cutters are guided in corresponding tracks which extend at equal distances on the thus produced prosthesis surface whose final outline has already been finish worked.
The drawback is here that with this method it is possible only to create shapes which can be developed into a plane. Moreover, the grooved shaft must have been prefabricated in its basic exterior shape before the grooves are cut.